1. Field of the Invention
This invention relates to fluid flow systems and, more particularly, to such systems employing positive displacement pumps.
2. Description of the Prior Art
A major problem involved in providing operational gas-turbine-powered automobiles lies in the different operating characteristics of the turbines, contrasted with presently-conventional power plants. No greater skill for competent operation of a gas-turbine-powered vehicle should be required than that for conventional vehicles; and, ideally, the controls and handling characteristics should appear the same to the driver.
One of the prime objectives of the automotive gas turbine control system is to obtain handling characteristics similar to those encountered in internal combustion power plants. Various approaches have been suggested, but most suffer from the fact that turbine engine control is compounded by the existence of two degrees of freedom--fuel flow and turbine nozzle orientation--as opposed to the single degree of freedom of the conventional combustion engine. While the present invention is not concerned with turbine nozzle orientation, apparatus suitable for use with an electronic computer is providing for regulating the fuel flow.
Steady state engine control requirements can be segregated into the two areas of fuel flow regulation and nozzle position control, corresponding to the two degrees of freedom. Expressed in simplest terms, the requirement reduces to inputting a particular engine fuel flow rate, and adjusting the nozzle position to assure optimum engine performance. The rate of engine fuel flow is essentially determined by the vehicle driver, with the control system performing a limiting function with respect to driver fuel demands. One suggested method of fuel flow modulation is to use an open loop type schedule wherein delivered engine fuel flow is a direct function of foot pedal (throttle) position. However, the characteristics of a regenerated engine are such that a substantial lag exists between the fuel flow disturbance and acquisition of gas generator steady state speed. Since gas generator speed is related directly to engine power, this lag can pose significant problems to the driver when stabilizing the vehicular velocity.
Conventional fuel delivery systems consist of a fuel pump and means for controlling fuel delivery to the engine. These functions are often accomplished by a positive displacement type fuel pump that is driven from the engine gear box, a flow control valve that modulates fuel flow to the engine, and a pressure relief valve that returns excess fuel flow to the pump inlet. The conventional hydromechanical fuel flow control valve is both complex and expensive.
U.S. Pat. No. 2,669,093 to Lee discloses a control apparatus for use with gas turbine engines. A planetary gear control mechanism provides an output in response to engine speed and a reference speed established by a hydraulic motor. A variable delivery fuel pump is driven by the engine. The pump is responsive to an output of the control mechanism to provide a varying fuel output to the engine. However, the Lee apparatus too is quite complex, and while perhaps acceptable for use in aircraft--for which it is designed--it is impractical for the mass--produced automotive market.
Other patents of which applicant is aware involving shaft speed control arrangements are U.S. Pat. Nos. 1,403,658 of Zweigbergk, 2,272,934 of Cotal and 2,847,876 of Willard.